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81 -Frequency Relay
Description
This frequency relay (81) includes three types of frequency elements, namely the overfrequency (81O), the under-frequency (81U), and the rate-of-change-of-frequency (ROCOF) (81R) elements. There are five levels of thresholds available with the 81O and 81U elements, whereas the 81R element features only one level.
Each level corresponds to a predefined frequency level and a tripping delay time. When the frequency or ROCOF monitored by the relay exceeds the settings, the relay operates. The model works for 50 Hz or 60 Hz system
The frequency relay operates whenever the frequency or ROCOF measured from the input voltage signals using a zero-crossing detection logic exceeds the preset settings.
A time delay is used to enable the relay to ride through momentary frequency fluctuations and thus prevent nuisance operation. The five-level characteristic of 81O and 81U are presented in Figures as shown below:
Characteristics of 81O
Characteristics of 81U
Mask and Parameters
General Parameters
The following parameters are tunable:
| Name | Description | Unit | Variable = {Possible Values} |
|---|---|---|---|
| Frequency | The nominal frequency of the measured voltage signals. | Hz | Freq_param= {50, 60} |
Freezing time | The freezing time of the 81 relay, when t < freezing time, | s | tunf_param = { [0.10, 60.00] } |
Settings - Overfrequency
The following parameters are tunable:
| Name | Description | Unit | Variable = {Possible Values} |
|---|---|---|---|
| Enable Overfrequency | Overfrequency element enable/disable | - | Enable_81O_param= {0, 1} |
| Level 1 | Over-frequency level 1. | Hz | OLevel1_param={ [45, 55] } for 50 Hz Operation; { [55, 65] } for 60 Hz Operation. |
| Level 2 | Over-frequency level 2. | Hz | OLevel2_param= { [45, 55] } for 50 Hz Operation; { [55, 65] } for 60 Hz Operation. |
| Level 3 | Over-frequency level 3. | Hz | OLevel3_param= { [45, 55] } for 50 Hz Operation; { [55, 65] } for 60 Hz Operation. |
| Level 4 | Over-frequency level 4. | Hz | OLevel4_param= { [45, 55] } for 50 Hz Operation; { [55, 65] } for 60 Hz Operation. |
| Level 5 | Over-frequency level 5. | Hz | OLevel5_param= { [45, 55] } for 50 Hz Operation; { [55, 65] } for 60 Hz Operation. |
| Time 1 | Time delay associated with Level 1. | s | OTime1_param= { [0, 600] } |
| Time 2 | Time delay associated with Level 2. | s | OTime2_param= { [0, 600] } |
| Time 3 | Time delay associated with Level 3. | s | OTime3_param= { [0, 600] } |
| Time 4 | Time delay associated with Level 4. | s | OTime4_param= { [0, 600] } |
| Time 5 | Time delay associated with Level 5. | s | OTime5_param= { [0, 600] } |
Settings - Underfrequency
The following settings are tunable:
| Name | Description | Unit | Variable = {Possible Values} |
|---|---|---|---|
| Enable Underfrequency | Underfrequency element enable/disable | - | Enable_81U_param= {0, 1} |
| Level 1 | Under-frequency level 1. | Hz | ULevel1_param= { [45, 55] } for 50 Hz Operation; { [55, 65] } for 60 Hz Operation. |
| Level 1 | Under-frequency level 2. | Hz | ULevel2_param= { [45, 55] } for 50 Hz Operation; { [55, 65] } for 60 Hz Operation. |
| Level 1 | Under-frequency level 3. | Hz | ULevel3_param= { [45, 55] } for 50 Hz Operation; { [55, 65] } for 60 Hz Operation. |
| Level 1 | Under-frequency level 4. | Hz | ULevel4_param= { [45, 55] } for 50 Hz Operation; { [55, 65] } for 60 Hz Operation. |
| Level 1 | Under-frequency level 5. | Hz | ULevel5_param= { [45, 55] } for 50 Hz Operation; { [55, 65] } for 60 Hz Operation. |
| Time 1 | Time delay associated with Level 1. | s | UTime1_param= { [0, 600] } |
| Time 1 | Time delay associated with Level 2. | s | UTime2_param= { [0, 600] } |
| Time 1 | Time delay associated with Level 3. | s | UTime3_param= { [0, 600] } |
| Time 1 | Time delay associated with Level 4. | s | UTime4_param= { [0, 600] } |
| Time 1 | Time delay associated with Level 5. | s | UTime5_param= { [0, 600] } |
Settings - ROCOF
The following settings are tunable:
| Name | Description | Unit | Variable = {Possible Values} |
|---|---|---|---|
| Enable ROCOF | ROCOF element enable/disable | - | Enable_ROCOF_param= {0, 1} |
| Level 1 | Rate-of-change-of-frequency level. | Hz/s | Rf_param= { [-10, 10] } |
| Time 1 | Time delay associated with Level 1. | s | rocofDelay_param= { [0, 600] } |
Inputs, Outputs and Signals Available for Monitoring
Inputs
| Name | Description |
|---|---|
| Vabc | A 3-dimension voltage input for three-phase voltages, in the order of Va, Vb and Vc |
| Reset | The reset signal for the relay. The relay will be reset when this signal becomes 1. |
Outputs
| Name | Description |
|---|---|
| 81O | The output of over-frequency relay. By default it is 0, if an over-frequency scenario is detected, it becomes 1. |
| 81U | The output of under-frequency relay. By default it is 0, if an under-frequency scenario is detected, it becomes 1 |
| 81R | The output of rate-of-change-of-frequency relay. By default it is 0, if an under-frequency scenario is detected, it becomes 1. |
Sensors
| Name | Description | Unit |
|---|---|---|
| m | The calculated frequency by the relay/the actuating quantity of the relay. | Hz |
Typical Values for Parameters
The parameter section shows the possible values for each parameter. These values would change to fit the situation of the 81 relay model so they cannot be taken as sole values for each parameter.
| Name | Description | Unit | Typical value |
|---|---|---|---|
| Frequency | The nominal frequency of the measured voltage signals. | Hz | 60 |
Freezing | The freezing time of the 81 relay, when t < freezing time, | s | 0.2 |
| Enable Overfrequency | Overfrequency element enable/disable | - | Enabled |
| Level 1 | Over-frequency level 1. | Hz | 60.5 |
| Level 2 | Over-frequency level 2. | Hz | 61.0 |
| Level 3 | Over-frequency level 3. | Hz | 61.5 |
| Level 4 | Over-frequency level 4. | Hz | 62.0 |
| Level 5 | Over-frequency level 5. | Hz | 62.5 |
| Time 1 | Time delay associated with Level 1. | s | 2.0 |
| Time 2 | Time delay associated with Level 2. | s | 0.5 |
| Time 3 | Time delay associated with Level 3. | s | 0.4 |
| Time 4 | Time delay associated with Level 4. | s | 0.3 |
| Time 5 | Time delay associated with Level 5. | s | 0.2 |
| Enable Underfrequency | Underfrequency element enable/disable | - | Enabled |
| Level 1 | Under-frequency level 1. | Hz | 59.5 |
| Level 1 | Under-frequency level 2. | Hz | 59.0 |
| Level 1 | Under-frequency level 3. | Hz | 58.5 |
| Level 1 | Under-frequency level 4. | Hz | 58.0 |
| Level 1 | Under-frequency level 5. | Hz | 57.5 |
| Time 1 | Time delay associated with Level 1. | s | 2.0 |
| Time 1 | Time delay associated with Level 2. | s | 0.5 |
| Time 1 | Time delay associated with Level 3. | s | 0.4 |
| Time 1 | Time delay associated with Level 4. | s | 0.3 |
| Time 1 | Time delay associated with Level 5. | s | 0.2 |
| Enable ROCOF | ROCOF element enable/disable | - | Enabled |
| Level 1 | Rate-of-change-of-frequency level. | Hz/s | 0.3 |
| Time 1 | Time delay associated with Level 1. | s | 0.0 |
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